The field of the invention is illumination systems for photographic enlargers and the present invention is particularly concerned with multicolor picture enlargers.
The polyalkene and substituted polyalkene foams useful in the present invention are disclosed in Modern Plastics Encyclopedia published by MacGraw Publication Co, New York, N.Y., U.S.A.
It is known to the prior art to mount a mixing chamber preferably immediately before the negative stage for the purpose of uniformly illuminating the negative aperture, so that the light upon multiple reflections leaves the aperture as diffuse light as disclosed in U.S. Pat. No. 3,927,941 of Murray H. Simon. Such a chamber is simultaneously used in multicolor picture enlargers to achieve intensive color mixing.
Light-mixing boxes made of polystyrene foam have been found to be especially advantageous, because they are highly efficient for reflection and scattering. However, such boxes suffer from the drawback of heating up greatly in the presence of the contemporary conventional high output halogen lamps which act as point sources of light and heat. Furthermore these boxes create an undesired localization of heat barrier (high temperature) in the negative aperture. Again, the polystyrene material suffers from this concentrated heat after the equipment is used for longer periods. Such a light mixing box is disclosed in U.S. Pat. No. 3,897,147 of Haruki Yamaguchi.
To meet such shortcomings, a heat filter has been inserted into the beam after the lamp as disclosed in U.S. Pat. No. 3,831,021 of Leopold Muhlosser. But such filters are costly and affect the red region of the spectrum, which is important in color equipment, thereby also affecting the intensity of radiation. This in turn requires a filter correction in the color mixing section with ensuing loss of light. Therefore longer exposures are required. Another possible approach to prevent overheating the mixing box would be to use additional plates in front of it as disclosed in U.S. Pat. No. 3,897,147 of Murray H. Simon, but this approach too fails to eliminate the localization of heat and also causes loss of light.